Question

Explain the means by which mutations can result in an increase in complexity and order in species, and supply two examples of how complexity arose to support your answer.

Answer 1

Hugo de Vries and William Beteson described mutation as discontinuous heriditary variations causing major recognisable changes.

Mutations are different kinds

1) Gene mutation - If the changes occurs within one gene it can be called gene mutation.

2) Chromosomal mutation - If mutations occurs in several genes in the chromosome it is known as chromosomal mutation.

Only a very small percentage of mutations are beneficial.

Effects of mutation

Harmful mutations may cause genetic disorder.Mutation causing loss of a complex trait occur more often than mutations causing gain of a complex trait.

The survival and reproductive ability of individuals may be affected by mutations.In some cases the altered amino acid sequence of the protein may have negligible effect on the phenotype ,but other times it can have severe effects.Mutations are the main cause of diversity among organism.Mutations can change the genetic sequence.Some mutations affect only the individual that carries them,while others affect all of the carrier organism's offsprings.

The net result is the mutation rate probably does tend to increase with complicity ,although probably not fast enough to eliminate the cost of complicity.

Examples

1)Cystic fibrosis

A mutation in a single gene causes the body to produce thick and sticky mucus that clogs the lungs and blocks digestive ducts.

2) Another example is bar eye in Dorsophila melanogaster .In the normal flies the eyes are oval in shape. In some mutant forms the eyes are narrower( bar eye).It was found that this is due to the duplication of a gene in the X chromosome of the mutant individual.

Additional information

Gene mutations which result in the replacement of one amino acid by another one are known as missense mutations.Sometimes mutation may change the nucleotide sequence in a triplet code to a terminating codon.Such mutations are called nonsense mutations.